1. Field of Invention
The present invention relates to an apparatus and method for generating power and refrigeration simultaneously, more particularly, to an apparatus and method for generating power and refrigeration from low-grade heat.
2. Related Prior Art
As the technology advances and the global population grows, the demand for energy increases considerably. Excessive consumption of fossil fuel exhausts a huge amount of carbon dioxide that results in the green house effect that entails radical changes in the global weather. Hence, it has become a big challenge to the world to solve problems related to lack of energy resources and excessiveness of carbon dioxide, the green house gas. To solve these problems, there are two approaches, i.e., use of recyclable energy and reduction of the consumption of the fossil fuel. Regarding the effective use of the fossil fuel, efforts were made to reduce the consumption of the fossil fuel and increase conversion efficiencies in the past. Now, the recycling of waste heat seems promising because conversion technology has made a lot of progress.
High-grade waste heat, higher than 500° C., is recycled by combined cycle power generation or combined heat and power (“CHP”) for example. For low-grade waste heat that is often a byproduct of melting, drying, thermal treatment, vaporizing and combustion, there however has not been any economic and effective heat-recycling method. In general, the low-grade waste heat cannot directly be converted to another form for use in a factory or power plant, and is therefore directly released to the environment, with a few exceptions where it is recycled by heat exchangers or recuperators. The heat exchangers and recuperators must be carefully designed so that they can be compatible with the processes of production, and the low-grade waste heat can only be recycled and reused as heat.
Thus, an alternative, i.e., an organic Rankine cycle system is widely used to convert low-grade heat to high-grade energy, i.e., electricity power. The organic Rankine cycle system is the Rankine thermodynamic cycle which uses organic working fluid to generate electricity power. The Rankine cycle has been used in conventional steam power plants and steam engines for many years and is sometimes referred as a practical Carnot cycle undergoing working fluid phase change. The grade of ordinary waste heat is however too low to use the steam Rankine cycle for the electricity power generation. Therefore, water is replaced with another working fluid such as an organic solvent, and an organic Rankine cycle is formed to convert low-temperature waste heat to electricity power. Furthermore, a power plant based on the organic Rankine cycle could be developed to convert industrial waste heat, geothermal heat or even solar thermal heat to electricity power.
According to statistics made by Taiwan Power Company in the year of 2005, the consumption of electricity in residential areas is about 20% of the total consumption of electricity in Taiwan, and the consumption of electricity in commercial areas is about 11% of the total consumption of electricity in Taiwan. Most of the energy is consumed to provide air-conditioning and illumination in the residential and commercial areas. Therefore, conversion of low-grade heat to electricity and refrigeration is useful in solving the problems related to the lack of energy sources and the excessiveness of the green house gas.
Referring to FIG. 3, there is shown a conventional organic Rankine cycle apparatus 2 for recycling low-grade heat such as industrial waste heat, solar thermal energy and geothermal energy. The conventional organic Rankine cycle apparatus 2 includes a heating module 20, a power generator module 21, a condenser module 22 and a pressure pump 23. The heating module 20 includes a boiler 201 and a heat source 202. The heat source 202 is a source of low-grade heat such as industrial waste heat, solar thermal heat or geothermal heat. The power generator module 21 includes an expansion turbine 211 coupled to a power generator 212. The condenser module 22 includes a condenser 221 and a cooling tower 222. The boiler 201 is in connection with the expansion turbine 211. The expansion turbine 211 is in connection with the condenser 221. The condenser 221 is in connection with the pressure pump 23. The pressure pump 23 is in connection with the boiler 201. A working fluid is circulating in the conventional organic Rankine cycle apparatus 2. The working fluid may be an organic hydrocarbon, a small molecular inorganic compound (such as CO2 and NH3) or a chlorofluorocarbon. The heat source 202 provides the low-grade heat to the boiler 201 so that the boiler 201 vaporizes the liquid working fluid at constant pressure. With the vaporized working fluid expanding, the expansion turbine 211 drives the power generator 212 to generate electricity. Then, the vaporized working fluid pressure is turned from high to low. The cooling tower 222 sends a coolant such as water to the condenser 221 to condense the low-pressure vaporized working fluid to liquid constant pressure. The pressure pump 23 pressurizes the working fluid to the boiler 201 from the condenser 221. Thus, the conventional organic Rankine cycle apparatus 2 converts the low-grade heat to the electricity power. However, the conversion ratio is low. In addition, the conventional organic Rankine cycle apparatus 2 can only convert low-grade heat to electricity power.
To increase the conversion efficiency, another conventional organic Rankine cycle apparatus 3 has been disclosed referring to FIG. 4. The conventional organic Rankine cycle apparatus 3 includes an evaporator module 30, a power generator module 31, a condenser module 32, a pressure pump module 33 and a mixer 34. The evaporator module 30 includes three heat exchangers 301. The power generator module 31 includes two turbines 311 coupled to one power generator together. The pressure pump module 33 includes two pressure pumps 331. Thus, the conventional organic Rankine cycle apparatus 3 which becomes a single-loop multi-pressure system with circulated working fluid is able to reduce the irreversibility of the heat source and the system. With the mixer 34, superheated working fluid can be fully used so that the utilization efficiency and thermal efficiency are increased. The conventional organic Rankine cycle apparatus 3 however can only convert low-grade heat to electricity.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.